During flip chip semiconductor device assembly, a die, such as a microprocessor, is mounted on a substrate. A heat sink lid is then attached on top of the die and the substrate using a lid adhesive. The lid adhesive may be any commercially available adhesive, such as Lord MT-315 resin-based lid adhesive. The lid adhesive is applied in a predetermined dispense pattern in which some lid adhesive is applied to the substrate and other lid adhesive is applied to the die. It has been observed that when the lid adhesive is applied to the substrate, resin bleeds out of the lid adhesive and flows through to the bottom side of the substrate.
Dispensing resin-based lid adhesive directly over a ceramic substrate accelerates resin bleed-out. The capillary effect of the ceramic surface roughness drives the resin away from the adhesive matrix. The ceramic substrate essentially sucks up the resin from the adhesive. Previous solutions to this problem include the addition of a metal strip running around the edges of the substrate, which is intended to act as a barrier to prevent resin bleed-out at the edges of the substrate. This metal strip has proven to be ineffective for drastic bleed-out amounts.
Also, the metal strip does not prevent resin bleed-out through the bottom of the substrate. The bottom of the substrate comprises land grid array (LGA) pads that are electrically connected to the die. The resin that bleeds out of the lid adhesive on the top side of the substrate flows through the substrate and wicks up the LGA pads. This resin bleed out is a defect that cannot be left on the device after assembly. The resin bleed-out 02 must be manually erased from the LGA pads before the device is tested.
One disadvantage of the prior art is the loss in manufacturing time caused by the need to clean the resin bleed-out from the package. Flip chip microprocessors and similar semiconductor devices are produced in a high volume. Detecting and cleaning resin bleed-out cause production delays and requires extra personnel, which adds to the cost of production. Each device must be visually inspected for resin bleed-out, failed parts must be separated out, resin bleed-out must be erased from the device, and debris from the resin bleed-out erasures must be cleaned from the device.
A second disadvantage caused by resin bleed-out is potential contamination of the test board used to test the completed devices. If resin bleed-out remains on the LGA pads and the device is placed in a socket on a test board, the resin is likely to transfer to the test socket, which, in turn, could also contaminate all subsequently tested devices.